The present invention relates generally to ink storage containers for ink-printing systems, and more particularly to an ink storage container for an ink printing system having an ink-printing head, which can be arranged on the ink storage container. The present invention also relates to a method for producing such an ink storage container.
Ink-printing systems with ink-printing heads that function according to piezoelectric or thermoelectric principles are generally known. In such ink-printing systems, an ink-printing head is moved along an image support, using an electric motor drive device. A print image is generated on the image support by character-dependent excitation of the ink-printing head. Ink is supplied to the ink-printing head from an ink storage container, which is either stationary or is moved along the image support together with the ink-printing head. In this way, the ink-printing head can form an interchangeable module with the ink storage container.
If the ink-printing head is moved together with the ink storage container in the form of a printing module, the capacity of the ink storage container is limited due to the drive forces required and limitations on the size. Care is necessary to ensure that in spite of great dynamic stress, the ink supply to the ink-printing head from the ink storage container is not interrupted. The ink storage container must also be structured so that complete utilization of the ink in the ink supply container is possible for an efficient printing operation.
U.S. Pat. No. 4,771,295 discloses an ink storage container with an integrated thermoelectric printing head. The ink storage container and the ink-printing head form a single structural unit in the form of a printing module, which is arranged on a printer carriage of the printing system. The entire housing of the ink storage container is filled with a porous material of polyurethane foam, which exhibits a controlled porosity. At the bottom of the ink storage container, an ink extraction opening in the form of a collar-shaped connection part that extends into the ink storage container is provided. This part is sealed off with regard to the porous material by means of a metal mesh grid. This serves to prevent penetration of air bubbles and dirt particles into the ink supply system. The porous material of polyurethane foam is pressed into the housing under pressure, so that a compression zone results in the immediate vicinity of the connection region. The pore size of this compression region is less than that in a region of the foam farther removed from the connection region. The aim of this measure is to increase the capillary forces in the area surrounding the connection region, so that ink can be reliably fed to the connection region.
The pipe-shaped connection region which projects into the container space reduces the ink supply that can be utilized. Furthermore, there is the risk that because of the small size of the connection region in comparison with the entire supply, the mesh grid will clog with air bubbles and therefore block the ink supply. Due to the foam compression, there is also the risk that singular regions with capillary behavior that deviate from one to the next will be formed. This could cause ink islands to form in the foam. Complete emptying of ink from the foam is therefore only possible within certain limits. Complete emptying furthermore presupposes that the foam is completely saturated with ink. Depletion zones have a detrimental effect on ink transport.
In the ink storage container disclosed in U.S. Pat. No. 4,771,295, the pipe-shaped ink collection region extends significantly into the housing. Therefore, part of the housing volume cannot be utilized to hold a storage element and therefore to store ink. Furthermore, the danger of ink clogging exists when the ink is extracted relatively rapidly.
Finally, the ink storage container disclosed in U.S. Pat. No. 4,771,295 requires defined compression of the storage element in the region of the filter element to guarantee targeted ink flow in the direction of the ink collection region. This can give rise to singular regions, each with a capillary behavior that differs from that of one or more of the others, which can lead to ink islands.
The present invention is directed to the problem of developing an ink storage container for an ink-printing system, in which the ink storage container has an ink-printing head assigned to it, which has a simple design avoiding the problems of the prior art, which allows as complete emptying of the ink as possible, and in which penetration of air bubbles into the ink supply system of the ink-printing head can be reliably prevented, without any interruption in the ink supply. The present invention is also directed to the problem of developing a method for producing such an ink storage container for an ink-printing system.